This research project is aimed at an identification of the number, rate, and type of complications of prehospital cardio-pulmonary resuscitation. C.P.R. as currently practiced prehospital, is a necessary emergency technique which always includes external chest compression and ventilation. It frequently includes definitive emergency medical measures such as endotracheal or esophageal intubation, defibrillation and intravenous medication. Each manuever has a strong potential for unintended and unanticipated injurious consequences. This project will describe the type, severity, and incidence of specific complications in 3 study sites (Baltimore, Miami, and Seattle) and examine the relationship between victim and rescuer characteristics, rescue technique and the rate and type of complications. Recommendations will be made regarding technique and training in an effort to reduce the number and severity of complications.